Radioactive waste left over from decades of weapons production has received much of the public attention at the Idaho National Engineering and Environmental Laboratory's buried waste site.

But INEEL scientists and engineers contend the cancer-causing solvents they are quietly cleaning up pose the greater short-term threat to the Snake River Plain Aquifer - Idaho's Lake Erie-sized underground water source.Crews are using a technology called recuperative flameless thermal oxidation, said Lynn Higgins, project manager with Parson's Infrastructure Technology Inc.

The method involves three giant vacuum cleaners sucking contaminant vapors out of the ground from holes drilled about 100 feet deep.

"We're taking care of a problem before it becomes so widespread and costly that it will take many more millions of dollars to clean up," said Patti Kroupa, U.S. Department of Energy cleanup pro-ject manager.

The solvent waste is from leaky containers dumped from the early 1950s through the 1960s in about 20 acres of pits and trenches at the INEEL's Radioactive Waste Management Complex. Earlier records are sketchy, but officials know workers buried 9,000 barrels of solidified carbon tetrachloride, trichloroethylene and perchloroethylene between 1966 and 1970.

The solvents were used in production of nuclear warheads at the government's Rocky Flats, Colo., weapons plant.

Most of the contamination has been found in a sediment bed about 240 feet underground. But traces of solvent waste also have turned up 580 feet down in the main aquifer, in all 10 test wells encircling the dump site.

The cleanup method involves heating vapors drawn to the surface to the point where they are destroyed. The only emissions are carbon dioxide, water and trace amounts of hydrogen chloride gas.

"We've chosen this to be environmentally friendly so we don't have a secondary waste stream," said Eric Miller, project manager with Lockheed Martin Idaho Technologies Co., the INEEL's main contractor.

About 40,000 pounds of solvent have been removed since the system was installed in December 1996.

The project's cost initially was estimated at $54.2 million through 2002, but Kroupa said the expense probably will be much lower.